1. Field of the Invention
The present invention relates to a carbon fiber-reinforced carbon composite material composed of carbon as a matrix and carbon fiber as a reinforcement, and also to a process for producing the same.
2. Description of the Prior Art
Carbon fiber-reinforced carbon composite material is referred to as C/C material. It is used as a heat-resistant material in the fields of spacecraft and aircraft. The process for producing the C/C composite material is disclosed in U.S. Pat. Nos. 3,734,797 and 4,201,611; British Patent No. 1,360,887; Japanese Patent Laid-open Publication Nos. 62768/1974 and 101985/1979; and Japanese Patent Publication No. 25094/1987. According to one of the disclosed processes, the C/C composite material is produced in the following manner. At first, a preform of nonwoven fabric or woven fabric is impregnated or coated with pitch or a thermosetting resin such as phenolic resin, furan resin, and epoxy resin, thereby to form a prepreg. A plurality of the prepregs are laminated on top of the other to form a multi-layer product. The layers are made into a unified body by press molding or the like. The unified body is calcined so that the matrix resin is carbonized and graphitized. If necessary, the impregnation and calcination are repeated to increase the density of the composite material. According to the other disclosed process, the C/C composite material is produced by the steps of laminating nonwoven fabrics by needle punching, thereby forming a preform, impregnating the preform with a resin, and calcining and carbonizing the impregnated preform.
The above-mentioned process has a disadvantage that the pitch or thermosetting resin does not permeate into the filament yarns (composed of 1000 to 4000 filaments) which constitute the nonwoven fabric or woven fabric. Thus the resulting C/C composite material is liable to cracking at the fiber-matrix interface and also to delamination. Moreover, the C/C composite material produced by the above-mentioned process has locally unbalanced strength which leads to delamination and deformation during use.
In order to overcome these disadvantages, a new C/C composite material has been developed. It is produced by mixing a matrix raw material (such as thermosetting resin) with short fiber to give a prepreg, and molding and calcining the prepreg. The thus produced short fiber-reinforced carbon composite material is poor in strength and impact resistance because the fiber region is small and the fiber-to-fiber distance is large. An additional disadvantage of this composite material is that the strength in the direction parallel to the surface is smaller than in the direction perpendicular to the surface.